Stabilized polyoxymethylenes



United States Patent 3,394,102 STABILIZED POLYOXYMETHYLENES Ryoichi Wakasa, Shinichi Ishida, and Hiromiclii Fukuda,

Tokyo, Japan, assignors to Asahi Kasei Kogyo Kabushiki Kaisha, Osaka, Japan, a corporation of Japan No Drawing. Continuation-impart of application Ser. No. 300,914, Aug. 8, 1963. This application Oct. 7, 1966, Ser. No. 584,978

6 Claims. (Cl. 26045.8)

ABSTRACT OF THE DISCLOSURE A stabilized composition of a polyoxymethylene having a molecular weight of at least 20,000 and at least one hydantoin of the formula:

cn)..-on 0 I a 1 GHz H-N N-H wherein n is an integer from 2 to 5.

This application is a continuation-in-part of our earlier application Ser. No. 300,914 filed Aug. 8, 1963, now abandoned.

This invention relates to a process for stabilizing polyoxymethylene having a molecular weight of at least 20,000.

It is known that pure anhydrous formaldehyde can be polymerized to produce polyoxymethylene by the action of a polymerization catalyst, light, or a radioactive ray in the presence or absence of an inert solvent. Also trioxane which is a cyclic trimer of formaldehyde can be polymerized by the action of a catalyst or a radioactive ray. Polyoxymethylene produced by the above proc esses is known to decompose to produce monomeric formaldehyde. Accordingly, as is shown in Japanese Patent Pub. No. 5,439/59, 5,440/59, 3,886/61, processes comprising adding a stabilizer have been used. These processes are uneconomical and the polymer thus stabilized must be carefully washed. The above-said processes include adding such organic compounds as cited hereinunder. In such a case, the stabilizer is added during the polymerization or is added to the polyoxymethylone before the processing. Such stabilizers include:

(a) hydrazine, stabilized hydrazine and hydrazide (b) secondary or tertiary aromatic amines (c) phenols or substituted phenol (d) urea, thiourea and the substituted products thereof (e) polycarboxylic acid amides.

However, the effects of the above known stabilizers are insufiicient for practical purposes. Moreover, polyoxymethylene treated with the above-said stabilizers is liable to produce a colored mould after being processed.

We have found that hydantoins are especially suitable as stabilizers for polyoxymethylene having a molecular weight of at least 20,000 and such polyoxymethylene can be stabilized by admixing hydantoin to only such an extent that not only is the polyoxymethylene not colored, but in fact the degree of whiteness is increased. Accordingly, a mould having a greater degree of whiteness than that of any known stabilized polyoxymethylene is obtained.

This invention is based on the above-said discovery and includes a process for stabilizing polyoxymethylene having a molecular weight of at least 20,000 which com- 3,394,102 Patented July 23, 1968 wherein n is an integer from 2 to 5.

The above-said hydantoins include 5,5-tetramethylenespiro-hydantoin, 5,5-pentamethy1ene spiro hydantoin, 5,5-hexamethylene spiro hydantoin, and. 5,5-heptamethylene spiro hydantoin.

The above-said hydantoin is used either alone or in mixed form, and in combination with the other well known stabilizers described in (a)(e) above, such as phenol, aromatic amines, urea derivatives or hydrazine derivatives in the presence or absence of an organic solvent such as carbon tetrachloride, methylene chloride, pentane, heptane, tetrahydrofuran, diethylether, acetone, methyl ethyl ketone, methanol, ethanol, toluene, benzene; said solvent may contain 'water.

The amount of the stabilizer to be added is determined based on the effect of the hydantoin added and the properties of the polymer to be stabilized. The stabilizer is employed in a range from about 0.01 to 50% by weight, generally in the range from 0.1 to 20% by weight.

According to the process of the invention, polyoxymethylene mould having an excellent stability and excellent degree of whiteness can be economically and easily produced by a simple process comprising admixing hydantoins which are easily available and are generally stable into the polyoxymethylene before processing.

The details of the process of the invention are better understood from a consideration of the following examples which are merely given for the sake of illustration.

EXAMPLE 1 Thermal decom- Hydantoin added position velocity Property of mould (weight part) of polymer K (percent/min.)

5,?pentiasnethylene spiro hydan- (l. 79 Uniformly white.

oln,

5,5-pentan1ethylene spiro hydan- 0.60 D0.

toin, 5.3. 5,5-pentamethylene spiro hydan- 0. 49 Do.

toin, 10.0. 5,5-pentamethylene spiro hydan- 0. 20 Do.

toin, 25.0.

Norm-The product produced by acetylating the above-said polyoxymethylene per so with acetic acid anhydride in the presence of pyridine wafi stabillized up to K =0.20%/min., but the product showed a pale ye ow c0 or.

What is claimed is: 1. A composition comprising a high molecular weight polyoxymethylene having a molecular weight greater than 20,000 and at least one hydantoin of the formula:

wherein n is an integer from 2 to 5.

2. A composition as claimed in claim 1, wherein said hydantoin, is 5,S-tetramethylene-spiro-hydantoin.

3. A composition as claimed in claim 1, wherein said hydantoin is 5,5pentamethylene-spiro-hydantoin.

4-. A composition as claimed in claim 1 wherein said hydantoin is 5,5-hexamethylenespiro-hydantoin.

5. A composition as claimed in claim 1 wherein said hydantoin is 5,5-heptamethy1ene-spiro-hydantoin.

6. A composition as claimed in claim 1 wherein said hydantoin is present in an amount of 0.01%50% by weight.

References Cited UNITED STATES PATENTS DONALD E. CZAIA, Primary Examiner.

15 M. I. WELSH, Assistant Examiner. 

